1. Field of the Invention
The present invention pertains to equipment and methods for image processing, and more particularly, to image processing equipment and methods suitable for detecting moving objects and for assessment of complex visual fields containing moving objects, including assessment of the distance between a moving object and a reference point in such a visual field.
2. Prior Art.
Video cameras offer a number of advantages as input devices for systems which rely on visual data. They are lightweight, relatively inexpensive and can be used in a variety of hostile environments which humans tolerate poorly, or not at all. Video cameras find wide application in security and surveillance systems, for process control, assembly control, customer and personnel monitoring, as well as for many other uses. For example, by means of a television system, one guard can monitor an extensive area, indoors and outdoors, from a climate controlled room. When real time monitoring is unnecessary, video signals from one or more cameras can simply be recorded on magnetic tape and viewed later as the need arises.
Despite the above described advantages of the video camera input devices, however, conventional video based surveillance and intrusion detection systems, motion sensors, monitoring systems and the like present one significant drawback in that someone must constantly view one or more video displays whenever real time monitoring is necessary. For this reason, it becomes expensive to operate these systems. In view of this shortcoming, various attempts have been made to develop systems whereby reliable computer analysis of video signals can be achieved, thereby permitting unattended automated or semiautomated operation.
Conventionally, methods and devices for detecting moving objects, and for assessment of visual fields containing moving objects have involved application of various types of mathematical operations to sequentially obtained images from a video camera. Examples include methods wherein sequentially obtained images of a given visual field are analyzed by using Fourier transform and digital or analog filtering techniques so as to determine whether there is an moving object in a frame.
Because of the complexity of most video signals, with any of the above described methods, in order to obtain reasonably precise and reliable results, high speed numerical processing equipment is an absolute necessity, especially when real time analysis is desirable. Consequently, conventional systems for analysis of visual fields containing moving objects have been very costly due to the expense incurred for the requisite high speed data processing facilities. Furthermore, the selectivity of conventional equipment of this type has been inadequate, with the result that spurious results are quite common with use thereof, particularly so when used under circumstances where the background is complicated and moving such as in outdoor applications. This problem relates to the fact that presently available methods and equipments are fundamentally based on a methodology for detecting a foreign object out of a visual field obtained at cirtain time. In other words, the theoretical background of the above mentioned conventional methods and equipments have not been based on the concept to detect an abnormal conditions based on the analysis of stationary time series.
One additional drawback of conventional motion detecting and monitoring devices and methods is that generally a single video camera is used for each visual field, for which reason only two dimensional data is provided. Accordingly, when distance factors are of importance, these systems tend to be inadequate. When monitoring hazardous areas, for example, when someone appears to be approaching the point of danger, distance data is helpful for evaluating the urgency of a response to the situation, a feature which the conventional devices do not offer.